U.S. Fireflies Flashing in Unison

Science News,  March 13, 1999  by Susan Milius

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A rare, dazzling spectacle may not be limited to far-flung places

A dark tree spangled with fireflies adorned the cover of the Aug. 31, 1991, issue of SCIENCE NEWS. Reader Lynn Faust of Knoxville, Tenn., still remembers it.

Hoping to read about the showy displays of the Great Smoky Mountains, Faust flipped to the cover article (SN: 8/3/91, p. 129). She learned that male Asian fireflies gather by the thousands in trees, flashing on and off in unison. The article disturbed her, however. "No matter how I read it, it seemed to mean that there were no real synchronous fireflies in the United States," she recalls.

What about the June ritual that she and her family regularly enjoyed at their cabin in the mountain resort of Elkmont, Tenn.? Around 10:30 at night, the family, sometimes 18 people representing three generations, would wrap themselves in blankets and sit silently on the unlit porch.

As eyes adjusted to the darkness, the yard appeared to twinkle with a natural light show. Dozens of fireflies flickered five to eight times, then all went dark for about 6 seconds only to burst into light again. And again. And again. In the background, fireflies high on a hillside started their sequence just a little ahead of the ones below, so light rippled down. "It looks like a waterfall of fireflies," Faust says.

"I didn't realize nobody knew they were there," she chuckles. She had always assumed that other vacationers in the mountains crowded onto their own porches on midsummer nights to watch the lights wink on and off.

After reading the SCIENCE NEWS article, however, Faust contacted firefly researcher Jonathan Copeland of Georgia Southern University in Statesboro. He's one of the current lightning bug devotees who study such questions as how the insects' internal pacemakers coordinate the show and how such fireworks evolved.

When Copeland and his colleagues visited the cabin, they found that the grassy hillsides with a handy creek support an unusual abundance of the firefly Photinus carolinus. Instead of relying on subjective thrills of watching the show, the researchers worked their way through videotapes, frame by frame, monitoring points of light appearing and disappearing in the blackness. Yes, the males definitely synchronize their flashes, Copeland says. "It makes you wonder how many more synchronic fireflies we'd find out there if we'd just leave our air-conditioned houses."

A few other reports of synchronous U.S. fireflies have flickered through the scientific literature. A Texas species, Photinus concisus, dazzled Dan Otte of the Academy of Natural Sciences in Philadelphia in the 1970s. The most common East Coast backyard flasher, Photinus pyralis, may not synchronize for more than a few cycles at a time in the wild, but when confined in a laboratory cage, males can pick up the beat and flash with each other.

Since the description of the Tennessee flasher, other coordinated displays have turned up. Faust, an avid amateur naturalist who has been searching for leads to other examples, has herself found at least three more mountain spots where P carolinus displays. The species seems to range along the Smokies at elevations around 2,000 feet and has been reported as far north as Pennsylvania. So, Faust was not surprised to get a late-night call from a woman with a cell phone standing bedazzled among synchronizing fireflies on the lawn of a North Carolina mountain fishing lodge.

One night in 1997, while walking the dog on Skidaway Island outside Savannah, Ga., Copeland's wife, Ursula Sterling, spotted a different coordinated display among yet another species of fireflies. Researchers have tentatively identified her find as Photuris frontalis, a species reported from Gulf states like Louisiana and Florida north to South Carolina.

A couple of months later, Copeland saw the same coordinated display twinkling in Congaree Swamp National Monument in South Carolina. He'd been tipped off by park naturalist Fran Rametta, who'd heard of the Elkmont display and began wondering about the light shows he had witnessed among the massive century-old swamp trees at night.

Questioning how fireflies synchronize "does not come easily to us as human beings because we accept our own ability to dance or to march in unison as being second nature," argued John Buck in his classic 1976 SCIENTIFIC AMERICAN article. Yet for the rest of nature, Buck considers this kind of synchrony--coordinating rhythmic actions in a group--very rare.

Other animals certainly can act in a coordinated way. They might respond to the same stimulus, such as when a flock of gulls startles and takes to the air in a single whoosh. Some creatures, like fish swimming in a school, can coordinate their spacing and zip off in the same direction as if connected by wires.

Yet, synchronized repeated motions are much rarer. The gulls that take off in a flock match wing beats only for a few measures. Buck points out that horses in harness don't match steps on their own. Beyond the foot-stomping, hand-clapping, Riverdancing throngs of humanity, he can think of only a few creatures that show tight, spontaneous synchrony: certain chorusing insects like crickets and katydids and, of course, some of the fireflies.